Today, radio frequency filters are widely used in electronic devices in order to filter a certain frequency/-range from noise frequencies or the like. There exist a number of different types of radio frequency, RF, filters, and a certain type of radio frequency filters is a ceramic filter that may cover the frequency bands from 40 MHz to 5 GHz. These filters are therefore especially suitable for applications in devices of cellular communications systems or in WLAN equipment. However, ceramic filters may be used in all different kinds of electronics. By using ceramic radio frequency filters, the radio frequency filters may be shrunk substantially.
A radio frequency filter is assembled by arranging filter parts, such as pucks, discs, rods or the like, into a rigid housing or a sheet metal housing. In some radio frequency filters, a good electrical contact between the housing and the filter part is required for the radio frequency filter to work appropriately with a desired performance. A method of producing a good contact is done by soldering the elements of a radio frequency filter together.
One way of solving the demands for a good contact is also by creating parts with very good tolerance. This will however affect the price on the product.
As filters installed in electronic devices, such as base stations or the like, operate in temperature varying environments the housing of the radio frequency filters tends to move in relation to the filter part, due to, for example, different thermal expansion coefficients of the materials in the housing and the filter part, different shapes and dimensions or the like. In ceramic filters, the thermal expansion of the ceramic part differs substantially from the thermal expansion of the sheet metal. The filter elements expand and shrink differently resulting in that the elements tend to move back and forth relative each other wearing out the soldered seam keeping the elements in contact. This is due to the tensile and compressive forces that arise due to the willing to move relative another. The worn out soldered seam results in a poor electrical contact between the housing and the ceramic material reducing the performance of the radio frequency filter.
This may be solved by creating a force from an external screw. Adding a force from a screw to the assembly makes the assembly unnecessary big. A screw requires a thicker or more robust structure to support the forces generated from the screw. The use of a screw arrangement will result in a force that generates a contact between ceramic rod and the metal housing, but there will also be a reaction force on the perimeter between an end plate and the housing part that may create unwanted gaps.